1. Field
Aspects of the present disclosure relate generally to wireless communications, and more particularly, to multipath transport control in a wireless communication network.
2. Background
The transmission control protocol (TCP) is a transport protocol frequently used for non-real-time services such as HTTP for web browsing, FTP, IMAP, etc. A TCP connection can be set up between a client, e.g., user equipment (UE), and a server. TCP is above the IP layer, and uses retransmissions, flow control, and congestion control to improve the reliability of the IP layer.
For flow control, the receiver side in a TCP connection controls the transmitter so that only as much data is sent as the receiver has a buffer capacity for. Thus, the transmitter side dynamically adjusts the transmission rate in accordance with acknowledgements from the receiver. Further, congestion control at the transmitter side may use a congestion window (CW) controlled by slow start and congestion avoidance algorithms and an offered window with the size the receiver has a buffer for, to determine the amount of data the transmitter side can transmit.
In a modern network such as the Internet, hosts are often connected by multiple paths, where each path is defined by a source and destination address pair. For example, a mobile station may include multiple wireless links such as WWAN links for two or more protocols such as W-CDMA, LTE, CDMA2000, and WiMAX, and possibly a WLAN or WPAN link. Similarly, a network server may have any number of links to the network.
However, TCP restricts communications to a single path per transport connection. To improve the efficiency of resource usage within the network, a multipath TCP protocol has been described in order to enable these multiple paths able to be concurrently used by splitting the information over multiple transport paths. By using more than one path, multipath TCP can enhance user experience through improved resilience to network failure and increased throughput.
The information being routed over the TCP connection includes data and control signaling. Control messages may include any information exchange to setup up or maintain multiple paths, such as inquiring about additional IP addresses to set up a multipath connection. Data information includes application layer data being communicated over multipath transport.
While multipath TCP provides various improvements, there remains a desire to further improve data and control signaling delivery, particularly for connections over multiple paths including wireless links which may have independently varying signal qualities. That is, with such a multipath connection, the exchange of control messages may be hindered when the path carrying those control messages fails due to a deep fade on the corresponding wireless link. Here, multipath session setup and maintenance can be delayed. Further, when data on one path fails, starvation may occur on another, good path, hindering application performance and user experience.